In electronic or automatic toll collection applications, it is desirable to correctly identify a vehicle traveling on the roadway with minimal operator intervention. Furthermore, it is often necessary to read the vehicle license plate number included within an image or multiple images of a vehicle for billing and enforcement purposes. The images are obtained when a vehicle travels through a toll gate or an enforcement gateway. The toll gate may or may not have a device capable of physically blocking the passage of vehicles, such as a mechanical arm. The requirement to capture license plate images exists for lane based and open-road (no lane barrier) electronic toll collection systems. The license plate reading operation is typically performed using an automatic optical character recognition (OCR) system, a manual system, or a combination of both systems. Both OCR and manual reads are subject to errors which degrade performance and reduce revenues of the toll collection system. Automatic reading errors are typically different from human operator manual read errors, and two different operators viewing the same license plate image sometimes read different license plate numbers.
Some toll collection systems employ transponders to identify a vehicle automatically as it passes through a toll collection point. Sometimes the transponder is moved to an unauthorized vehicle or has been stolen from a vehicle. In such a situation it is useful to determine the license plate number(s) on the vehicle. In other toll collection systems it is not feasible to equip all vehicles, for example, vehicles which make sporadic use of the toll roadway, with a transponder. Furthermore, there is a need to read license plates in the event of transponder read failures to increase system reliability and to maintain billing revenues.
In automatic toll systems, incorrect identification of a vehicle or non-identification of a vehicle is costly. In conventional systems, the error rate ranges from two percent to ten percent. An error in a license plate reading results in lost revenue, increased customer support expenses and customer dissatisfaction when the customer is incorrectly billed. When a vehicle license plate cannot be identified, the toll revenue is not collected.
Conventional systems require multiple reads of every license plate image to verify that the plate is correct. This is a costly solution because typically at least one of the read operations must be performed manually by an operator. Other systems allow errors to be posted to customer accounts and wait for the customers to complain. Some of the plate reading problems can be corrected by manually reading the license plates. In a manual read operation, a human operator typically reads the license plate number from a stored image of the rear end of a vehicle having a license plate. The license plate image is captured at the time the vehicle traveled through a toll collection point or enforcement gateway. However the cost of manually reading a license plate is relatively expensive, and manual reading is not feasible for reading large numbers of license plates. Both conventional automatic license plate reading systems and conventional systems incorporating manual reading of images of license plates have inherently different problems reading license plate images. Operators manually reading a large number of license plates are subject to fatigue and are prone to an error rate which increases with the number of license plates read during a workday. Automatic image collection and processing is subject to image misreads, equipment malfunction and periodic maintenance.
It would, therefore, be desirable to read license plates with a minimal error rate and a minimum number of manual reads. It would be further desirable to effectively use license plate numbers read manually by a group of operators to minimize the error rate of an automatic license plate reading system and to utilize additional information collected on a vehicle's trip through an roadway having an automatic toll collection system to reduce the license plate reading error rate and the number of manual reads.